Avionics Air Cooling (AAC), because of a distributed system approach, provides for individually tuned equipment heat removal configurations. Airborne heat loads reject to the moderate temperature Internal Thermal Control System (ITCS). With selectable fan speed and ITCS flow, the cooling system with associated distribution ducting provides cooling and circulation in non-habitable zones.This selectivity as well as packaging considerations within the rack, potential fire detection responsibilities and varied pressure drops added to the air return of the system present a challenge to the user. Air balancing recommendations and an analysis of the hardware and its selectability defines the full range of operation to meet these responsibilities and provides a common procedure for test.This paper will address the overall air balancing recommendations and orifice plate techniques necessary for the user to perform system optimization. Packaging and general instrumentation requirements are defined from these techniques.